-LRB- CNN -RRB- -- For better or worse , Iraq and the United States have been attached at the hip for decades .

From the 1991 Gulf War to the 2003 invasion that toppled Saddam Hussein to subsequent years marred by violence and instability , there 's no doubting the deep connection between the two nations . That 's largely thanks to policies crafted out of Washington , be they intended to contain or eliminate Hussein or to stabilize and build up the fragile nation that remained in his wake .

So it is no surprise that , with militants overrunning much of Iraq and threatening its capital , people are turning to the United States .

What can it do ? What will it do ?

Among Obama 's options :

Option No. 1 : Send in American troops

As of Monday , the Pentagon says it has only about 170 troops in Baghdad and 100 in undisclosed locations around the region . Their job is to protect the U.S. Embassy and other American interests , the Pentagon said .

That 's far from the troop levels of past Iraq engagements .

U.S. troops did n't stay in Iraq for long after driving Hussein 's military out of Kuwait in 1991 , but they did hunker down 12 years later after toppling the Baathist regime . The responsibility that comes with rebuilding a country from over 6,000 miles away was one factor , but so was the continued violence .

American troop levels in Iraq peaked at 166,300 in October 2007 , according to the U.S. Defense Department .

Critics derided the withdrawal of U.S. troops by the end of 2011 . Among them was Sen. John McCain , who last week reiterated his disgust at that decision and called for the firing of Obama 's national security team in part over what 's happened in Iraq .

`` Could all this have been avoided ? '' the Arizona Republican said about the current state of Iraq , though he did n't outright call for fresh military action . `` And the answer is : Absolutely yes . ''

The biggest , simplest way to make an impact in Iraq : Send American troops back into the country .

But it wo n't happen again .

Iraqi Foreign Minister Hoshyar Zebari told CNN on Thursday that no one is calling for `` American troops into Iraq . '' And of all options now on the table , it 's the only one that the Obama administration has explicitly nixed .

`` We are not contemplating ground troops , '' White House Press Secretary Jay Carney said last week . `` I want to be clear about that . ''

Option No. 2 : U.S. airstrikes

Still , while the U.S. military might not have a role fighting on the ground in Iraq , it could have a role over it .

On Monday , Secretary of State John Kerry acknowledged to Yahoo! News that airstrikes on Iraqi targets are under consideration .

The aircraft carrier USS George H.W. Bush and five other warships are now in the Persian Gulf . More than 500 Marines and dozens of helicopters are on standby .

In the past , Iraqis have been very public about their desire to limit the involvement of the American military . Yet , a U.S. official said the Iraqi government had indicated a willingness for the U.S. military to conduct airstrikes targeting members of the Islamic State in Iraq and Syria -LRB- ISIS -RRB- and other militants .

American air power has proven effective before in campaigns such as Kosovo or Libya .

Yet it 's not foolproof .

Last week , Carney deflected a question about whether Obama might consult Congress before sending warplanes into Iraq -- saying it 's too early to give an answer because the President has n't decided the best course of action yet .

Attacking sites from the air comes with a host of limitations and challenges -- the risk of U.S. casualties or capture should warplanes be shot down ; the unlikelihood of wiping out an insurgency from above ; the likelihood militants will blend into the civilian population and cause death and injury to the innocent .

Option No. 3 : Provide more military aid

Unlike the first two options , the U.S. government has already taken this course and has signaled it may do more .

A Defense Department official says that about $ 15 billion in equipment , training and other services already have gone to Iraq . Carney reeled off some of the many items that have made their way east of late : millions of rounds of small arms fire , thousands of rounds of tank ammunition , hundreds of Hellfire missiles , grenades , assault rifles , helicopters and much more .

And that tally does n't include an additional $ 1 billion in arms -- including up to 200 Humvees -- that are now in a 30-day review period in Congress .

But U.S. officials -- calling the current situation `` extremely urgent '' -- acknowledge that what 's already in Iraq and what 's coming may not be enough .

Chief among those officials is Obama himself , who said last week : `` Iraq is going to need more help from us , and it 's going to need more help from the international community . ''

At the same time , it 's not like the billions of dollars worth of firepower proved all that effective against ISIS fighters in places like Mosul , Iraq 's second-largest city . Witnesses reported seeing Iraqi security forces drop their weapons , even shed their uniforms , then run to safety .

James Jeffrey , U.S. ambassador to Iraq from 2010 to 2012 and now a fellow with the Washington Institute for Near East Policy , characterized Iraq 's military as `` ill-trained , badly led and not particularly competent . ''

`` They clearly can not fire and maneuver , '' said Jeffrey , a U.S. Army veteran .

And it 's not just a matter of making sure that whatever resources sent to Iraq are used effectively and not wasted . Already , militants have been able to pick up weaponry , vehicles and other goods on its swift , vast sweep of Iraq -- some of it supplied by the United States .

`` We are not surprised , '' a defense official told CNN . `` It was a question of when , not if , something like this would happen . ''

Option No. 4 : Effect change politically in Iraq

Beating back ISIS by retaking Mosul and other cities would be a huge victory for Iraq 's government .

But it would n't be a complete , conclusive win unless the country can get its house in order . And doing that , according to experts and U.S. officials , requires addressing what CNN 's Nic Robertson has referred to as Iraq 's `` political dysfunction . ''

One silver lining to the turmoil is Prime Minister Nuri al-Maliki 's government seems to be coordinating with the semiautonomous Kurdish government , American officials said . It appears Iraqi forces will team up with Kurdish fighters , known as the Peshmerga , to combat ISIS .

Addressing the divisions between Shiites and Sunnis , the two dominant Muslim sects , in Iraq is another matter .

Al-Maliki 's government , as well as the military , is dominated by Shiites -- leaving Sunnis not only left out but also bitter , so much so that some of them may not see ISIS as a worse option .

`` Over the last several years , we have not seen the kind of trust and cooperation develop between moderate Sunni and Shia leaders inside of Iraq , '' Obama said . `` That accounts in part for some of the weakness of the state , and that carries over into the military . ''

Vice President Joe Biden has been talking regularly with al-Maliki to try to effect political change , including possibly through a new unity government that gives Sunnis a prominent , hands-on role .

Still , words -- as opposed to , say , troops on the ground -- are sometimes only so effective . And it 's not like al-Maliki has heeded U.S. officials ' call for sectarian reconciliation and unity in the past .

Yet Washington 's misgivings about the Prime Minister do n't change the fact that they support him , generally . The question is still how , exactly , they will support him .

`` There 's more that Prime Minister Maliki should have done , could have done , over the course of time , '' said State Department spokeswoman Jen Psaki . `` That 's a message we 've conveyed publicly and privately to him .

`` But the enemy here is -LRB- ISIS -RRB- . We need to work together and present a united front . ''

Interactive : Where is Iraq 's oil ?

ISIS : The first terror group to build an Islamic state ?

The siege of Mosul : What 's happening ?

Recording : ISIS promises more fighting in more Iraqi cities

CNN 's Barbara Starr contributed to this report .

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The U.S. has a long history in Iraq , including the 1991 Gulf War and 2003 invasion

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As Iraq battles radical Islamist militants , U.S. officials have promised more help

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Air strikes and additional weaponry and aid are among the options being mulled

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But ground troops have been ruled out , according to a White House spokesman